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Texas Instruments SN74HCT645PW
- Part No.:
- SN74HCT645PW
- Manufacturer:
- Texas Instruments
- Package:
- 20-TSSOP (0.173", 4.40mm Width)
- Datasheet:
-
SN74HCT645PW.pdf
- Description:
- IC TXRX NON-INVERT 5.5V 20TSSOP
- Quantity:
- Payment:
- Shipping:
Inventory:530
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Product details
Overview
SN74HCT645PW from Texas Instruments is an octal bus transceiver with direction control and 3-state outputs, operating at 4.5 V to 5.5 V, delivering ±6-mA drive strength, 14 ns typical propagation delay at 5.5 V, and TTL-compatible inputs - used for bidirectional data routing between microcontroller buses and peripheral subsystems in industrial control modules.
For engineers reviewing the SN74HCT645PW datasheet, SN74HCT645PW pinout, SN74HCT645PW application, or SN74HCT645PW equivalent, key selection criteria include direction-control logic behavior, 3-state isolation timing (ten = 22 ns, tdis = 23 ns at 5.5 V), thermal resistance (θJA = 83°C/W), and TSSOP-20 package compatibility with high-density PCB layouts.
Technical Context
This device implements asynchronous bidirectional data transfer using a single DIR input to select A→B or B→A path, and an active-low OE input to enable/disable all outputs simultaneously into high-impedance state. It uses HCT logic family silicon with CMOS input structure and bipolar-compatible output stages.
Each of the eight transceiver channels supports independent signal flow under shared DIR/OE control; no internal latching or clocking is present - operation is purely combinatorial and level-sensitive. Input thresholds are fixed at VIH = 2.0 V and VIL = 0.8 V across full VCC range, ensuring robust noise margin against TTL-level sources.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Supply Voltage | 4.5 V to 5.5 V - ensures compatibility with standard 5-V TTL/CMOS systems without level-shifting. |
| Propagation Delay | 14 ns typical at 5.5 V, CL = 50 pF - enables reliable operation in sub-20-ns timing-critical bus interfaces. |
| Output Drive | ±6 mA at 5 V - sufficient to directly drive 15 LSTTL loads, eliminating need for external buffers in legacy designs. |
| Input Current | ≤1 µA max - minimizes loading on upstream logic and reduces static power in battery-backed or low-power hold modes. |
| 3-State Enable Time | 22 ns max (ten) at 5.5 V - defines minimum interval between OE assertion and valid output, critical for bus arbitration timing. |
| Thermal Resistance | θJA = 83°C/W (TSSOP-PW) - informs derating requirements for sustained 8-channel switching in enclosed industrial enclosures. |
| Logic Compatibility | TTL-voltage inputs (VIH = 2.0 V, VIL = 0.8 V) - allows direct interfacing with 5-V microcontrollers, FPGAs, and legacy peripherals. |
Pinout & Package
TSSOP-20 package (PW), 6.5 mm × 4.4 mm body, 0.65 mm lead pitch, 1.2 mm max height, exposed pad not present, RoHS-compliant NIPDAU finish, MSL Level-1.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1 | DIR | Direction control input: LOW routes B→A, HIGH routes A→B - determines real-time data flow polarity. |
| 2–9 | A1–A8 | Input/output port A side - connects to microcontroller or master bus; driven when DIR/OE conditions permit. |
| 10 | GND | Ground reference for all I/O and internal logic - must be low-impedance connection to minimize ground bounce. |
| 11 | VCC | Positive supply (4.5–5.5 V) - powers internal logic and output drivers; requires local 0.1-µF bypass capacitor. |
| 12 | OE | Active-low output enable - drives all A/B outputs into high-Z when HIGH, enabling bus sharing. |
| 13–20 | B1–B8 | Input/output port B side - connects to peripheral or slave bus; electrically isolated when OE = HIGH. |
Key Features
| Feature | Design Value |
|---|---|
| Asynchronous bidirectional data path | Enables real-time A↔B bus communication without clocks or handshaking - ideal for legacy ISA-style or custom parallel interfaces. |
| High-current 3-state outputs | ±6 mA drive per channel supports direct fanout to multiple LSTTL inputs, reducing component count in industrial backplane designs. |
| Low static power consumption | 80 µA max ICC - allows use in always-on monitoring circuits where quiescent current must remain below 100 µA. |
| TTL-compatible input thresholds | VIH = 2.0 V / VIL = 0.8 V ensures interoperability with 5-V microcontrollers (e.g., MSP430, C2000) and FPGA I/O banks without external biasing. |
| Controlled output transition times | tr/tf ≤ 14 ns (CL = 50 pF) limits EMI generation and prevents false triggering on adjacent traces in mixed-signal PCBs. |
Applications
| Industrial PLC Backplane Interface | Legacy Microcontroller Bus Expansion |
|---|---|
|
Use Scenario: Bidirectional data exchange between a main CPU module and distributed I/O cards over a 20-pin parallel bus in a DIN-rail mounted PLC chassis. IC Role / Device Role / Timing Role: SN74HCT645PW acts as a direction-controlled bus buffer, isolating CPU and I/O domains while supporting read/write cycles via DIR and OE coordination. Use Value: Enables deterministic 14-ns latency for status polling and command writes, meeting <50-ns cycle time requirements of IEC 61131-3 soft-PLC runtimes. |
Use Scenario: Extending GPIO bandwidth of an MSP430F5xx MCU by connecting eight additional digital sensors via a parallel sensor array with shared address/data lines. IC Role / Device Role / Timing Role: SN74HCT645PW serves as a programmable bus transceiver, allowing the MCU to read sensor states or write configuration bits through the same physical pins. Use Value: Eliminates need for discrete MOSFET switches or multiplexers, reducing BOM cost and layout area while maintaining full 5-V logic compatibility. |
| Automotive Body Control Module (BCM) | Test Equipment Digital Pattern Generator |
|
Use Scenario: Interfacing a CAN controller's parallel diagnostic port to a microcontroller-based BCM during production calibration and firmware update sequences. IC Role / Device Role / Timing Role: SN74HCT645PW provides galvanically isolated bidirectional data coupling between two 5-V domains, controlled by BCM firmware via DIR/OE. Use Value: Supports fast, glitch-free bus turnaround during flash programming - verified with 23 ns disable time (tdis) preventing bus contention during mode transitions. |
Use Scenario: Generating synchronized 8-bit stimulus patterns for DUT testing in automated bench systems using a PC-connected FPGA pattern generator. IC Role / Device Role / Timing Role: SN74HCT645PW functions as a configurable output latch interface, translating FPGA I/O to robust 5-V TTL levels with precise edge alignment. Use Value: Delivers ±6 mA drive into 50-Ω coaxial cabling, preserving signal integrity up to 25 MHz without external line drivers. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar octal transceiver applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| SN74HCT245PW | Identical pinout and function but lacks DIR inversion logic - DIR = HIGH enables A→B only; no B→A mode. | Suitable only for unidirectional or software-managed bidirectional protocols requiring separate control lines. | Select SN74HCT245PW if direction is fixed per session and board space permits simpler control logic. |
| 74LVC245APW | Lower voltage range (1.65–3.6 V), higher speed (tPD = 4.2 ns), but incompatible with 5-V systems without level translation. | Applicable in modern 3.3-V embedded systems; not drop-in replaceable in existing 5-V designs. | Choose 74LVC245APW only for new 3.3-V designs prioritizing speed and power efficiency over legacy voltage compatibility. |
Compared with SN74HCT645PW, SN74HCT245PW simplifies control at the cost of bidirectional flexibility, while 74LVC245APW offers superior performance in 3.3-V domains but requires full system voltage redesign - making SN74HCT645PW the sole option for robust, pin-identical 5-V bus bridging with runtime direction reversal.
Availability
SN74HCT645PW is available at Aetrix Electronics and suitable for industrial PLC backplanes, automotive BCM diagnostics, test equipment pattern generation, and legacy microcontroller bus expansion requiring stable component supply and long-term manufacturability.
Supply support for SN74HCT645PW includes scheduled delivery planning, volume procurement assistance, BOM continuity management, traceable sourcing, and lifecycle availability coordination for OEM customers, industrial embedded developers, connected-device designers, and electronics production programs.
Manufacturer
Texas Instruments is a global semiconductor leader founded in 1930, specializing in analog, embedded processing, and logic solutions for industrial, automotive, and communications markets.
The SN74HCT645PW belongs to TI's 74HCT logic family - designed specifically for 5-V mixed-signal systems requiring TTL-compatible inputs, low power, and robust bus isolation in harsh electromagnetic environments.
FAQ
What is the maximum operating temperature range for the SN74HCT645PW?
The SN74HCT645PW is rated for operation from −40°C to +85°C ambient temperature, matching industrial-grade requirements. This range is validated per TI's recommended operating conditions and supported by thermal characterization showing θJA = 83°C/W in the TSSOP-PW package - enabling reliable use in sealed enclosures without forced airflow.
Does the SN74HCT645PW support hot insertion or live bus swapping?
The SN74HCT645PW does not include explicit hot-swap protection circuitry. Its absolute maximum ratings allow VI and VO from −0.5 V to VCC + 0.5 V, and IO clamp current is ±20 mA, but bus contention during live insertion may exceed safe limits. For hot-swap applications, external series resistors or dedicated hot-swap controllers should be used alongside SN74HCT645PW.
Can the SN74HCT645PW be used with 3.3-V microcontrollers?
The SN74HCT645PW requires a 4.5–5.5 V supply and is not 3.3-V compatible. Its inputs are TTL-voltage referenced (VIH = 2.0 V min), so a 3.3-V controller may not reliably drive it high. To interface with 3.3-V logic, use a level translator such as TXB0108 or design with SN74LVC245APW instead - SN74HCT645PW itself must operate at 5 V.
What is the purpose of the DIR and OE pins on the SN74HCT645PW?
DIR (pin 1) selects data direction: LOW enables B→A transfer, HIGH enables A→B transfer. OE (pin 12) is an active-low output enable - when HIGH, all A and B outputs enter high-impedance state, isolating both buses. Together, they allow dynamic, software-controlled bidirectional communication without external gating logic - a core capability of SN74HCT645PW.
Is the SN74HCT645PW pin-compatible with other packages of the same part number?
Yes - SN74HCT645N (PDIP), SN74HCT645DW (SOIC), and SN74HCT645PW (TSSOP) share identical pinout and electrical functionality. The TSSOP-PW package has the same 20-pin arrangement and signal mapping as shown in the top-view diagram, enabling direct PCB footprint substitution where board space and thermal constraints permit.
SN74HCT645PW Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Texas Instruments
- Series:
- 74HCT
- Package/Case:
- 20-TSSOP (0.173", 4.40mm Width)
- Packaging:
- Bulk
- Product Status:
- Active
- Logic Type:
- Transceiver, Non-Inverting
- Number of Elements:
- 1
- Number of Bits per Element:
- 8
- Input Type:
- -
- Output Type:
- 3-State
- Current - Output High, Low:
- 6mA, 6mA
- Voltage - Supply:
- 4.5V ~ 5.5V
- Operating Temperature:
- -40°C ~ 85°C (TA)
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- 20-TSSOP
SN74HCT645PW FAQ
1.How can I place an order for SN74HCT645PW through Aetrix?
Please submit a Request for Quotation (RFQ) for SN74HCT645PW on Aetrix. Our sales agent will provide a competitive quotation and guide you through the order confirmation once you accept the terms.
2.Are the price and stock information for SN74HCT645PW reliable?
The price and inventory of SN74HCT645PW are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SN74HCT645PW is usually 5 days.
3.What payment methods are accepted for SN74HCT645PW?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for SN74HCT645PW transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for SN74HCT645PW?
SN74HCT645PW orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your SN74HCT645PW order is processed, you will receive an email with the shipment details and tracking number.
Note: Tracking information may take up to 24 hours to appear. Express delivery typically takes 3–5 business days.
5.How can I obtain technical support or documentation for SN74HCT645PW?
For technical support, including SN74HCT645PW datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SN74HCT645PW requirements.
6.How does Aetrix verify that SN74HCT645PW is sourced from the original manufacturer or authorized distributors?
All SN74HCT645PW products on Aetrix are procured from qualified distributors and authorized channels. Our dedicated quality assurance team conducts strict verification, including traceability checks and, if necessary, third-party testing. This ensures that SN74HCT645PW meets industry standards.
7.What is the process for return or replacement of SN74HCT645PW?
All SN74HCT645PW units undergo pre-shipment inspection (PSI). If there is an issue with SN74HCT645PW, returns or replacements are accepted under the following conditions:
1.Quantity discrepancies, incorrect items, or visible external defects (such as breakage or corrosion), acknowledged by Aetrix.
2.The issue is reported within 90 days of delivery.
3.The SN74HCT645PW part is unused and in its original packaging.
Return procedure for SN74HCT645PW:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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